After the rice crop is harvested on a farm in Nakhon Pathom province, a flock of around 10,000 ducks is released from a pen and instinctively stream towards the flooded fields to devour pests such as snails hiding in the rice stubble.

Drone footage, capturing the spectacle that resembles naturally-occurring animal migration, shows the birds zig-zagging across the fields as they head towards the nutrient-rich rice paddies without any guidance.

This way of raising ducks in rice-growing areas has long been a tradition in the area and other parts of the region.

Thais call it "ped lai thoong", which means "field chasing ducks".

The Khaki Campbell ducks, a British breed, are brought to rice fields after 20 days in nursery and will be raised on the move for the next few months. After roaming free for about five months, they are returned to the duck farm to produce eggs for up to three years.

"The benefit [for the breeder] is that we reduce costs to feed the ducks," said Apiwat Chalermklin, 34, a breeder who took over the business from his father.

"And in return, for the rice farmers the ducks help eat pests from the farm and the farmers can reduce the use of chemicals and pesticides."

During a field-cleaning job he expects to last a week in this 67-hectare farm, Apiwat's ducks have found plenty of food such as cherry snails, weeds, and other small pests.

Apiwat has four flocks of ducks that move around different rice fields in the province where farmers typically cultivate three rice crops every year.

"They help eat golden apple snails and the remains of unwanted rice husks that remain in the field from the last harvest. The ducks also step on the rice stubble to flatten the ground and that makes it easier to plough," said rice farmer Prang Sipipat.